There are many types of sonar systems used for military, commercial, and recreational purposes. Generally, forward looking sonar systems are designed to build a 2 dimensional image along a single vertical or horizontal slice. More advanced systems are capable of building 3 dimensional images through a series of 2 dimensional pings pointed directly below the vessel with the direction of the 2 dimensional strip being perpendicular to the track of the vessel. This type of system is downward-looking and used for bottom mapping. At present commercial forward-looking navigation sonars in creating a 3 dimensional image from a single ping, having any array geometry are unknown.
In the field of interferometry, arrays of many receivers are used, which enable a user or an autonomous system controller to make precise angular measurements for long-range detection, imaging, object classification, obstacle avoidance, etc. The operating frequencies can vary between a few Hz for seismic applications to many Megahertz or Gigahertz for ultrasound and radio systems. The sensors are usually arranged in an array in order to improve the signal to noise ratio for better detection. In such an array, the receiver hardware must be replicated for each channel. Since the number of array elements can vary from a minimum of four to several thousand, the cost for the receiver hardware can be a real burden. Furthermore, in order to perform the additional operations required for detection, for example: beam forming and multi-beam processing; each sensor output must be connected to a central signal processor. Depending on the number of array elements, this can create a serious wiring burden. Finally, since the sensors detect analog signals while the central processing unit operates in the digital domain, each channel must be equipped with a high-resolution analog-to-digital converter (ADC). The complexity of these systems limit the ability to provide for upgrades and modifications and render repairs expensive.
Many accidents could have been avoided if the mariners were equipped with a 3 dimensional, forward-looking, bottom mapping and obstacle detection sonar with a fixed frame of reference for navigation. To be navigationally effective, the sonar must have a fast update rate. Depending on their size and sea conditions, ships can tilt and roll so much that the depths of obstacles including the seafloor detected with a phased array sonar can be tens of meters in error. Therefore, not only is advantageous to generate the 3 dimensional image with a single or small number of pings, it is also advantageous to display the image with a fixed frame of reference.